It depends on the shape of the container. If the container has no special features (basic cylinder), then it is just a straight line OR more likely a parabola. You need to know the surface of the bottom of the cylinder, and know the quantity of water poured each second into the cylinder. Then it is a basic multiplication/squaring.
If the container is some exotic shape, then the graph may take any possible shape.
Do you have any more information ? Maybe it might be a good idea to show us the illustration, I'm pretty sure it contains the information you need And don't try to hide it, I know you have an illustration